Influenza is a zoonotic disease, meaning it is a disease that can be transmitted from non-human animals to humans. There are three main types of influenza viruses and influenza A viruses are the ones that are primarily zoonotic, and are found in various animals including chickens, cats, pigs, and whales. The eradication of measles was made much easier due to the fact that the disease was only found in humans. Once an effective vaccine was created, eradication would rest mostly on the administration of the vaccine to a large swaths of the human population. Once a sufficient number of humans were inoculated to create herd immunity and with no chance of non-human animals spreading a new strain of measles, the disease became virtually eradicated. With the zoonotic nature of influenza, our close proximity to other animals through pets and the food supply makes new strains of influenza A much more likely to spread to humans and potentially causing a new epidemic.The rapid mutation and proliferation of influenza makes it very difficult to create a universal flu vaccine. Humans have extraordinarily robust immune systems that can mount defenseless against new and old pathogens. The issue with new pathogens like a new strain of influenza virus is that the body can take up to several days to ramp up an immune response. In that time, the virus can take hold in your body and begin replicating in your cells, resulting in illness. Vaccinations work on this basis to introduce and prepare your immune system to a particular virus by inoculating your body with a weak non-harmful version of the disease causing pathogen.
Like other vaccines, flu vaccines work by introducing a harmless weakened version of the disease causing virus or an antigen that illicit an immune response. Our immune system identifies a particular strain of an influenza virus by the proteins found on the surface of the viruses called hemagglutinin. The heads of these proteins mutate often, which creates hundreds of new strains of the flu virus each year and creating a constant cat and mouse game for researchers. Each year, a new flu vaccine is released with only three or four antigens out of potentially hundreds of different strains of the flu virus. The 2014-2015 flu vaccine only had a 23 percent success rate, while the 2015-2016 vaccine was estimated to be 60 percent effective. These large swings have largely to do with new strains that were not included in the flu vaccine. There is promising research involving broadly neutralizing antibodies that attack the stem of the hemagglutinin protein, which is less likely than the head to mutate. A vaccine created with a substance that can elicit an immune response involving these specific antibodies could potentially be a universal flu vaccine.
An average of 200,000 Americans are hospitalized each year due to influenza and between 3,000 and 49,000 people will die due to the flu. Historically, some of the most severe pandemics were caused by the influenza virus. While many other deadly diseases have been eradicated through vaccination and other efforts, influenza still remains a difficult disease to eradicate. The virus that causes influenza is constantly evolving and the zoonotic nature of the virus had made it very difficult for researchers to pin down a broad-scale vaccine. It remains that a new flu vaccine is released each year to combat the most virulent strains each flu season, but promising research involving broadly neutralizing antibodies may result in a universal flu vaccine.